1. Field of the Invention
The present invention relates to a stretched film excellent in low-temperature heat sealability after corona treatment as well as that before corona treatment, and/or in heat shrinkability.
2. Description of the Related Art
Polypropylene has been used widely in fields of films and sheets due to its excellent transparency, heat resistance and food sanitation. In particular, a material with low-temperature heat sealability is awaited in such fileds as food packaging.
For example, JP,2-57770,B discloses, as a material with low-temperature heat sealability, a laminated polypropylene film having an excellent low-temperature heat sealability, an excellent transparency, a low blocking and a good scratch resistance, in which a copolymer which is obtained by a specific polymerization method using a specific catalyst system, the copolymer containing a specific amount of a specific comonomer as a main component as a copolymerization component and containing a specific cold xylene-soluble portion and a specific boiling heptane-insoluble portion, is laminated as a heat sealable layer.
Publication of Japanese Patent No. 3070419 discloses a laminated polypropylene film having an excellent low-temperature heat sealability and an excellent hot tack property without losing a good transparency and a good blocking resistance, in which a random copolymer of propylene with an xcex1-olefin having 4 or more carbon atoms is laminated as a heat sealing resin, the random copolymer being obtained by use of a specific catalyst system and a specific polymerization method and having a specific comonomer composition, a specific molecular weight distribution, a specific cold xylene-soluble portion and a specific composition of cold xylene soluble portion.
However, in such fields as food packaging, the speed of package fabrication has recently been enhanced and therefore materials moreexcellent in low-temperature heat sealability after corona treatment as well as that before corona treatment have been awaited.
The object of the present invention is to provide a stretched film excellent in low-temperature heat sealability after corona treatment as well as that before corona treatment, and/or in heat shrinkability.
In view of the above-mentioned actual situations, the present inventors found, through their diligent investigation, that the above problem can be solved by a film stretched at least uniaxially, the film comprising a layer comprising a copolymer of propylene with xcex1-olefin and/or ethylene such that in measurement of a DSC curve the amount of the heat absorbed in the temperature range of from Txe2x88x9210 (xc2x0 C.) to T+10 (xc2x0 C.) accounts for from 15 to 36% of the amount of the heat absorbed in the temperature range of from 53 to 170xc2x0 C., wherein T denotes a temperature (xc2x0 C.) at which a maximum endothermic peak appears in the DSC curve.
In the present invention, the amount of the heat absorbed in the temperature range of from Txe2x88x9210 (xc2x0 C.) to T+10 (xc2x0 C.) is referred to as xe2x80x9cthe amount of the main heat absorbedxe2x80x9d, and the amount of the heat absorbed in the temperature range of from 53 to 170xc2x0 C. is referred to as xe2x80x9cthe amount of the total heat absorbed.xe2x80x9d